1. Field of Invention
This invention is directed to apparatus and methods of distributed object handling.
2. Description of Related Art
A traditional media handling system can move media, such as a sheet, from one location to another location along a path, while performing one or more operations on the sheet, such as inversion, image transfer or fusing. As shown in FIG. 1, a traditional media handling system 100 includes a controller 110 that controls multiple actuators 130, which perform operations on the sheet while moving the sheet along a paper path 140.
Typically, timing signals are used to coordinate the operations and sheet movement. For example, the sheet can be fed into the path 140 at a certain time according to a timing signal. The sheet can then move through the path 140, past various position sensors within a certain time window, and arrive at a transfer station at a specific time.
However, this traditional media handling system 100 is subject to the problem that when any temporal error in the operations beyond a certain tolerance is detected and flagged to the controller 110, the machine containing the traditional media handling system 100 is shut down. The traditional media handling system 100 does not include any feedback control. Thus, the actuators 130 need to be precisely manufactured, which is expensive. Also, because of this lack of feedback control, the traditional media handling system 100 does not perform well when subjected to different types of media, and has problems maintaining accuracy and reliability at high speeds.
A modular object handling system can overcome these problems via a more control-centric design, which can be accomplished by adding more controls. The use of control strategies, beyond the simple timing of the traditional media handling system 100, can also allow a wider range of objects, such as a wider range of media types, to be handled at higher speeds.
For example, a modular object handling system that includes a multi-level control architecture can provide advantages over the traditional media handling system 100 discussed above. This modular object handling system can include a system controller that coordinates the functions and/or the operations of individual module controllers, which in turn control corresponding actuators, to provide a desired system function, such as transporting objects along a path. In particular, the system controller can download an overall trajectory for each object to the module controllers. The module controllers can control their respective actuators to maintain each object on its planned trajectory while in that module.
The system controller performs the overall trajectory planning by taking the constraints of each of the module actuators into account. The trajectories planned by the system controller can then be provided as functions in distance-time space, such as cubic splines.
Deviations from an object""s desired trajectory typically occur during the operation of the modular object handling system. For minor deviations, all control can be left to the individual module controllers, since they may not be concerned with other module controllers or whether the overall control criteria are satisfied. However, the system controller is concerned with satisfying the overall control criteria. Thus, the system controller may constantly monitor the location of the objects and contemporaneously redetermine the objects"" trajectories using various control techniques to make up for such deviations.
However, continuously replanning trajectories by accessing complex trajectory redetermining techniques can be difficult to accomplish in real time. In fact, depending on the equipment and software involved, it may be necessary to resort to approximate determinations and heuristics to identify the effects of deviations and to replan the deviating trajectories in real time.
Thus, instead of continuously replanning the deviating trajectories, it may be desirable to use predetermined trajectories and trajectory envelopes to encode the various combinations of system constraints and task requirements. The trajectory envelopes can denote regions around other trajectories to indicate control criteria of interest, such as control and collision boundaries. By comparing the current state of an object with the predetermined trajectory envelopes, the system controller can quickly determine the extent to which the current state satisfies the control criteria.
For example, instead of continuously checking the distance between objects and redetermining the trajectories to avoid collisions, a predetermined collision envelope around the desired trajectory can be used. The predetermined collision envelopes are determined such that, as long as the objects are within their collision envelopes, the objects will not collide. A control envelope can similarly be used to determine other control criteria, such as whether the object will reach its target on time to accomplish a task requirement. This modular object handling system simplifies on-line determinations to merely include a comparison between a particular trajectory and the corresponding trajectory envelope, or between a current object position and a trajectory envelope.
The systems and methods discussed above predetermine a trajectory, as well as well as at least one predetermined trajectory envelope that is associated with the trajectory, for each object moving along the path. However, if the predetermined trajectory envelope is large and/or an the object deviates a large amount from the predetermined trajectory, then an unnecessarily large amount of energy may be exerted in attempting to place that object back on that object""s predetermined trajectory.
To avoid this, multiple trajectories, as well as trajectory envelopes associated with each of the multiple trajectories, can be determined for each object. The apparatus and methods of the invention can then monitor the status of each object, and switch between the multiple predetermined trajectories in order to actively improve energy usage efficiently. The apparatus and methods can also modify the trajectories of other objects to avoid collisions with the object whose trajectory was originally switched.
Other exemplary embodiments of the invention include determining the multiple trajectories, as well as the trajectory envelopes associated with each of the multiple trajectories. This determination can take various requirements of a trajectory envelope into account, such as ensuring that all relevant constraints remain satisfied as long as an object remains within the trajectory envelope, ensuring that the trajectory envelope is large enough so that the object will not leave the trajectory envelope under normal circumstances, ensuring that the earliest trajectory envelope corresponds to the earliest possible trajectory of an object, and ensuring that the latest trajectory envelope corresponds to the latest possible trajectory of an object.
A method of determining trajectories and trajectory envelopes, while also taking the trajectory envelope requirements discussed above into account, can include specifying a system model as well as system constraints and task requirements. A first nominal trajectory can be determined. Earlier nominal trajectories can then be determined, starting from the first nominal trajectory, by applying a safe object distance constraint backward, applying an expected error/deviation model, and/or solving a suitable subset of the constraints while optimizing for the earliest possible new trajectory. Later nominal trajectories can also be determined, starting at the first nominal trajectory, by applying a safe object distance constraint forward, applying an expected error/deviation model, and/or solving a suitable subset of the constraints while optimizing for the latest possible new trajectory. An envelope can also be determined for each of the determined nominal trajectories.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of various exemplary embodiments of the systems and methods according to this invention.